The invention relates to a process for the purification and recovery of particulate sulfur from a biological process for converting sulfur compounds. The invention more specifically relates to a sulfur recovery method which produces fine particle high purity sulfur retaining a selected amount of attached biomass which imparts hydrophilic properties to the sulfur.
A number of processes have been developed to biologically reduce the concentration of a sulfur compound in process streams involved in petroleum refining or other industrial processes. Many of these processes are directed toward reducing the concentration of sulfur compounds present in aqueous streams used to remove sulfur compounds from a flue gas or process stream. These aqueous streams are passed into a biological reaction zone in which a bacteria converts the sulfur compound into elemental sulfur. This is shown for instance in U.S. Pat. Nos. 5,354,545 and 5,518,519 issued to C. J. N. Buisman. The second patent shows the treatment of a gas stream in a scrubber with aqueous liquid which is biologically regenerated and returned to the scrubber. Sulfur is recovered via a settling zone.
U.S. Pat. No. 5,637,220 also issued to C. J. N. Buisman illustrates a reactor for use in biological conversions. The patent points out that the biological agent can be part of a film on various carriers including particulate sulfur produced in the process.
U.S. Pat. No. 6,051,518 issued to K. C. Srivastava presents a microbial process for the regeneration of solid sulfide-containing catalysts. The patent includes a description of the LO-CAT(copyright) process, which is described as a prior art liquid redox process. The depiction of this process shows sulfur recovered from an aerobic reactor being pumped to a belt filter. Sulfur from this filter is them passed into a reslurry vessel and the slurry is passed into a separator. The sulfur is eventually melted and stored.
The invention is a method for recovering high purity small diameter particles of elemental sulfur having sufficient attached biomass to impart hydrophilic properties to the sulfur from a biological treatment process.
One broad embodiment of the invention may be characterized as a biological process for conversion of sulfur compounds to elemental sulfur and the recovery of a hydrophilic fine particle sulfur product, which process comprises passing an aqueous stream containing a sulfur compound into a biological reaction zone in which the sulfur compound is brought into contact with a bacteria at conversion promoting conditions under which the bacteria extracts sulfur from the sulfur compound, thereby forming elemental sulfur; removing a reactor effluent stream comprising water, biomass, particles of elemental sulfur and salts from the biological conversion zone and passing the reactor effluent stream into a separation zone in which water and biomass are separated from the reactor effluent stream to yield a separator effluent stream comprising particulate elemental sulfur and water; passing the separator effluent stream into a first centrifugal separation zone and removing water to yield a second separation zone effluent stream containing over about 50 wt % particulate elemental sulfur having attached biomass; admixing the second separation zone effluent stream with water to form a slurry containing less than about 15 wt % solids; passing the slurry into a second centrifugal separation zone and removing water to yield a third separation zone effluent stream containing over 50 wt % particulate elemental sulfur having attached biomass; drying the third separation zone effluent stream to yield agglomerated hydrophilic fine particle elemental sulfur which contains attached biomass.
The drawing is a simplified flow diagram of a process in which the gas stream of line 1 is scrubbed, the scrubbing solution is regenerated in bioreaction zone 6 and fine particles of elemental sulfur are recovered via line 22.